Heat exchanger

ABSTRACT

Ends of heat-transfer plates S 1 , S 2 , formed by bending folding plate blanks in a zigzag fashion along folding lines L 1 , L 2 , are cut in an angle shape, and flange portions  26  formed by folding apexes of the angle shape are superposed one on another and brazed in a surface contact state, thereby to form combustion gas passage inlets  11  and air passage outlets  16  along the two end edges of the angle shapes. Compared with brazing of separate flange members onto the cut surfaces of the apexes of the angle shapes, this fabrication not only dispenses with precise finishing of the cut surfaces, but also serves to increase the brazing strength.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger includinghigh-temperature fluid passages and low-temperature fluid passagesdefined alternately by alternately disposing a plurality of firstheat-transfer plates and a plurality of second heat-transfer plates.

BACKGROUND ART

Such heat exchangers have already been proposed in Japanese PatentApplication Nos.7-193208 and 8-275057 filed by the applicant of thepresent invention.

The above conventional heat exchangers suffer from the followingproblem: The partitioning between a high-temperature fluid passage inletand a low-temperature fluid passage outlet and the partitioning betweena low-temperature fluid passage inlet and a high-temperature fluidpassage outlet are achieved by bonding a partition plate by brazing to acut surface formed on the heat-transfer plate by cutting itsangle-shaped apex portion. For this reason, the bonded portions of thecut surface of the heat-transfer plate and the partition plate are inline contact with each other. To reliably perform the brazing, theprecise finishing of the cut surface is required, and moreover, even ifthe finishing is performed, it is still difficult to provide asufficient bonding strength.

The above conventional heat exchangers also suffer from the followingother problem: axially opposite ends of the heat-transfer plate are cutinto angle shapes to define the fluid passage inlet and outlet.Therefore, a drifting flow of fluid is generated from the outer sidetoward the inner side as viewed in a turning direction due to adifference between the lengths of flow paths on the inner and outersides as viewed in the turning direction in a region where a fluidflowing into the heat exchanger obliquely with respect to an axis in thevicinity of the fluid passage inlet is turned in the direction along theaxis, and in a region where the fluid flowing in the direction along theaxis is turned in an inclined direction with respect to the axis in thevicinity of the fluid passage outlet. For this reason, the flow rate onthe outer side as viewed in the turning direction is decreased, whilethe flow rate on the inner side as viewed in the turning direction isincreased, whereby the heat exchange efficiency is reduced due to thenon-uniformity of the flow rate.

The above conventional heat exchanger is formed into an annular shape byfolding a folding plate blank in a zigzag fashion to fabricate moduleseach having a center angle of 90° and combining four of the modules in acircumferential direction. However, if the heat exchanger is formed bycombination of a plurality of modules, the following problems arise: thenumber of parts is increased, and moreover, four bonded points among themodules are produced, and the possibility of leakage of the fluid fromthe bonded portions is correspondingly increased.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished with the above circumstancesin view, and it is a first object of the present invention to ensurethat a sufficient bonding strength is provided without a precisefinishing of the ends of the heat-transfer plate. It is a second objectof the present invention to suppress of a drifting flow of a fluidgenerated at fluid-direction changing portions in the vicinity of thefluid passage inlet and outlet of the heat exchanger thereby to preventa reduction in heat exchange efficiency. It is a third object of thepresent invention to decrease the number of parts of the heat exchangerand to maintain the leakage of the fluid from the bonded portions of thefolding plate blank to the minimum.

To achieve the above object, according to a first aspect and feature ofthe present invention, there is provided a heat exchanger, comprising aplurality of first heat-transfer plates and a plurality of secondheat-transfer plates disposed radiately in an annular space definedbetween a radially outer peripheral wall and a radially inner peripheralwall, and a high-temperature fluid passage and a low-temperature fluidpassage which are defined circumferentially alternately between adjacentones of the first and second heat-transfer plates by bonding pluralitiesof projections formed on the first and second heat-transfer plates toone another, axially opposite ends of each of the first and secondheat-transfer plates being cut into angle shapes each having two endedges, thereby defining a high-temperature fluid passage inlet byclosing one of the two end edges and opening the other end edge ataxially one end of the high-temperature fluid passage, defining ahigh-temperature fluid passage outlet by closing one of the two endedges and opening the other end edge at the axially other end of thehigh-temperature fluid passage, defining a low-temperature fluid passageoutlet by opening one of the two end edges and closing the other endedge at axially one end of the low-temperature fluid passage, anddefining a low-temperature fluid passage inlet by opening one of the twoend edges and closing the other end edge at the axially other end of thelow-temperature fluid passage, characterized in that flange portionsformed by folding one of apex portions of the angle shape are superposedone on another and bonded together, whereby the high-temperature fluidpassage inlet and the low-temperature fluid passage outlet arepartitioned from each other by the superposed flange portions, andfurther flange portions formed by folding the other apex portion of theangle shape are superposed one on another and bonded together, wherebythe high-temperature fluid passage outlet and the low-temperature fluidpassage inlet are partitioned from each other by the superposed furtherflange portions.

With the above arrangement, in the annular heat exchanger in which thefluid passage inlets and outlets are defined by cutting the axiallyopposite ends of the heat-transfer plates into angle shapes, the flangeportions formed by folding the apex portions of the angle shape aresuperposed one on another and bonded together, whereby the fluid passageinlet and outlet are partitioned from each other by bonding a partitionplate to the superposed flange portions. Therefore, as compared with thecase where a partition plate is bonded in a line contact state to thecut surfaces formed by cutting the heat-transfer plates, the superposedflange portions can be bonded together in a surface contact state,thereby not only increasing the bonding strength, but also eliminatingthe need for a precise finishing of the cut surfaces. Therefore, thebonding of the projections on the heat-transfer plates and the bondingof the flange portions can be accomplished in a continuous flow, leadingto a reduction in processing cost.

If a folding plate blank including the first and second heat-transferplates which are alternately connected together through first and secondfolding lines is folded in a zigzag fashion along the first and secondfolding lines, and portions corresponding to the first folding lines arebonded to the radially outer peripheral wall, while portionscorresponding to the second folding lines are bonded to the radiallyinner peripheral wall, the number of parts can be reduced, and moreover,the misalignment of the first and second heat-transfer plates can beprevented to enhance the processing precision, as compared with the casewhere the first and second heat-transfer plates are formed fromdifferent materials and bonded to each other.

If the flange portions are folded into an arcuate shape and superposedone on another, and the height of projection stripes formed alongangle-shaped end edges of the first and second heat-transfer plates isgradually decreased in the flange portions in order to close the fluidpassage inlets and outlets, it is possible to prevent a gap from beingproduced between the projection stripes, while preventing the mutualinterference of the projection stripes abutting against one another atthe flange portions to enhance the sealability to the fluid.

To achieve the first object, according to a second aspect and feature ofthe present invention, there is provided a heat exchanger, comprising aplurality of first heat-transfer plates and a plurality of secondheat-transfer plates which are formed into a rectangular shape, and ahigh-temperature fluid passage and a low-temperature fluid passage whichare defined alternately between adjacent ones of the first and secondheat-transfer plates by bonding a pair of long sides of each of thefirst and second heat-transfer plates to a first bottom wall and asecond bottom wall, bonding a pair of short sides of each of the firstand second heat-transfer plates to a first end wall and a second endwall, and further bonding a plurality of projections formed on the firstand second heat-transfer plates to one another, a high-temperature fluidpassage inlet and a high-temperature fluid passage outlet which aredefined in the first bottom wall so as to extend along the first andsecond end walls, respectively and which are connected to thehigh-temperature fluid passage, and a low-temperature fluid passageinlet and a low-temperature fluid passage outlet which are defined inthe second bottom wall so as to extend along the first and second endwalls, respectively and which are connected to the low-temperature fluidpassage, characterized in that flange portions formed by folding thepair of short side portions are superposed one on another and bondedtogether, and the first and second end walls are bonded to thesuperposed flange portions, respectively.

With the above arrangement, in the rectangular parallelepiped heatexchanger in which the pair of long sides of the pluralities of theheat-transfer plates formed into the rectangular shape are bonded to thebottom walls, respectively, while the pair of short sides are bonded tothe end walls, respectively, and the fluid passage inlets and outletsare defined at longitudinally opposite ends of the bottom walls, theflange portions formed by folding the short sides of the heat-transferplates are superposed one on another and bonded together, and the fluidpassage inlet and outlet are partitioned from each other by bonding thesuperposed flange portions to the end wall. Therefore, as compared withthe case where the end walls are bonded in a line contact state to endsurfaces formed by cutting the heat-transfer plates, the superposedflange portions can be bonded in a surface contact state to one another,thereby not only increasing the bonding strength, but also eliminatingthe need for a precise finishing of the cut surfaces. Therefore, thebonding of the projections on the heat-transfer plates and the bondingof the flange portions can be accomplished in a continuous flow, leadingto a reduction in processing cost.

If a folding plate blank including the first and second heat-transferplates which are alternately connected together through the first andsecond folding lines is folded in a zigzag fashion along the first andsecond folding lines, and portions corresponding to first folding linesare bonded to the first bottom wall, while portions corresponding to thesecond folding lines are bonded to the second bottom wall, the number ofparts can be reduced, and moreover, the misalignment of the first andsecond heat-transfer plates can be prevented to enhance the processingprecision, as compared with the case where the first and secondheat-transfer plates are formed from different materials and bonded toeach other.

To achieve the second object, according to a third aspect and feature ofthe present invention, there is provided a heat exchanger, comprising aplurality of first heat-transfer plates and a plurality of secondheat-transfer plates which are disposed radiately in an annular spacedefined between a radially outer peripheral wall and a radially innerperipheral wall, whereby a high-temperature fluid passage and alow-temperature fluid passage are defined alternately in acircumferential direction between adjacent ones of the first and secondheat-transfer plates, axially opposite ends of the first and secondheat-transfer plates being cut into an angle shape each having two endedges, respectively, thereby defining a high-temperature fluid passageinlet by closing one of the two end edges and opening the other end edgeat axially one end of the high-temperature fluid passage, defining ahigh-temperature fluid passage outlet by closing one of the two endedges and opening the other end edge at the axially other end of thehigh-temperature fluid passage, defining a low-temperature fluid passageoutlet by opening one of the two end edges and closing the other endedge at axially one end of the low-temperature fluid passage, anddefining a low-temperature fluid passage inlet by opening one of the twoend edges and closing the other end edge at the axially other end of thelow-temperature fluid passage, and tip ends of large numbers ofprojections formed on opposite surfaces of the first and secondheat-transfer plates being bonded together, characterized in that apitch of arrangement of the projections is different between the axiallyopposite ends and an axially intermediate portion of each of the firstand second heat-transfer plates.

With the above arrangement, in the annular heat exchanger in which thefluid passage inlets and outlets are defined by cutting the axiallyopposite ends of the heat-transfer plates into the angle shape, thepitch of arrangement of the projections formed on the heat-transferplate is different between the axially opposite ends and the axiallyintermediate portion of the heat-transfer plate. Therefore, it ispossible to prevent a drifting flow from being produced at afluid-direction changing portion to provide an enhancement in heatexchange efficiency and a reduction in pressure loss, by changing thefluid flow resistance in the vicinity of the fluid passage inlets andoutlets by the projections.

In areas facing the inlets and outlets of the high-temperature fluidpassage and the low-temperature fluid passage, if the pitch ofarrangement of the projections in a direction substantiallyperpendicular to the direction of flowing of fluid passed through theinlets and outlets is dense in an area portion nearer to a base endportion of the angle shape and sparse in an area portion nearer to thetip end portion, the flow resistance on a radially inner side of thedirection-changing portion where the fluid is easy to flow because ofthe short flow path can be increased by the dense arrangement of theprojections, and the flow resistance on a radially outer side of thedirection-changing portion where the fluid is difficult to flow becauseof the long flow path can be decreased by the sparse arrangement of theprojections, thereby preventing a drifting flow from being produced inthe fluid-direction changing portion to provide an enhancement in heatexchange efficiency and a reduction in pressure loss.

If the pitch of arrangement of the projections of the first and secondheat-transfer plates is set such that the unit number of heat transferis substantially constant in a radial direction at an axiallyintermediate portion of each of the first and second heat-transferplates, it is possible to radially uniformize the profile of temperatureof the heat-transfer plate to avoid the reduction in heat exchangeefficiency and the generation of undesirable thermal stress. When theheat transfer coefficient of each of the first and second heat-transferplates is represented by K; the area of each of the first and secondheat-transfer plates is represented by A; the specific heat of the fluidis represented by C; and the mass flow rate of the fluid flowing in theheat transfer area is represented by dm/dt, the unit amount N_(tu) ofheat transfer is defined by the following equation:

N _(tu)=(K×A)/[C×(dm/dt)]

If the projections are arranged at the axially intermediate portion ofeach of the first and second heat-transfer plates, so that they are notlined up in the direction of flowing of the fluid passed through theaxially intermediate portion, the fluid is agitated sufficiently by theprojections, leading to an enhanced heat exchange efficiency.

To achieve the second object, according to a fourth aspect and featureof the present invention, there is provided a heat exchanger, comprisinga plurality of first heat-transfer plates and a plurality of secondheat-transfer plates which are formed into a rectangular shape, anddisposed in parallel, so that a pair of long sides thereof are bonded toa first bottom wall and a second bottom wall and a pair of short sidesthereof are bonded to a first end wall and a second end wall, therebydefining high-temperature fluid passage and low-temperature fluidpassage alternately between adjacent ones of the first and secondheat-transfer plates, a high-temperature fluid passage inlet and ahigh-temperature fluid passage outlet which are defined in the firstbottom wall so as to extend along the first and second end walls,respectively and which are connected to the high-temperature fluidpassage, and a low-temperature fluid passage inlet and a low-temperaturefluid passage outlet which are defined in the second bottom wall so asto extend along the second and first end walls, respectively and whichare connected to the low-temperature fluid passage, and large numbers ofprojections formed on opposite surfaces of the first and secondheat-transfer plates and bonded together at tip ends of the projections,characterized in that the pitch of arrangement of the projections isdifferent between longitudinally opposite ends and a longitudinallyintermediate portion of each of the first and second heat-transferplates.

With the above arrangement, in the rectangular parallelepiped heatexchanger in which the fluid passage inlets and outlets are defined atthe longitudinally opposite sides of the rectangular heat-transferplates, the pitch of arrangement of the projections formed on each ofthe heat-transfer plates is different between the longitudinallyopposite ends and the longitudinally intermediate portion of theheat-transfer plate. Therefore, when the fluid is turned in the vicinityof the fluid passage inlet and outlet, the fluid flow resistance can becontrolled by the projections to prevent the generation of a driftingflow directed inwards in the turning direction to provide an enhancementin heat exchange efficiency and a reduction in pressure loss.

In areas facing the high-temperature and low-temperature fluid passageinlets and outlets, if the pitch of arrangement of the projections inthe direction substantially perpendicular to the direction of flowing ofthe fluid passed through the inlets and outlets is dense in an areaportion farther from the first and second end walls and is sparse in anarea portion nearer to the first and second end walls, the flowresistance on a radially inner side of the direction-changing portionwhere the fluid is easy to flow because of the short flow path can beincreased by the dense arrangement of the projections, and the flowresistance on a radially outer side of the direction-changing portionwhere the fluid is difficult to flow because of the long flow path canbe decreased by the sparse arrangement of the projections, therebypreventing a drifting flow from being produced in the fluid-directionchanging portion to provide an enhancement in heat exchange efficiencyand a reduction in pressure loss.

To achieve the third object, according to a fifth aspect and feature ofthe present invention, there is provided a heat exchanger, comprising aplurality of first heat-transfer plates and a plurality of secondheat-transfer plates which are disposed radiately in an annular spacedefined between a radially outer peripheral wall and a radially innerperipheral wall, whereby a high-temperature fluid passage and alow-temperature fluid passage are defined alternately in acircumferential direction between adjacent ones of the first and secondheat-transfer plates, a folding plate blank including the plurality offirst heat-transfer plates and the plurality of second heat-transferplates which are alternately connected together through first and secondfolding lines, the folding plate blank being folded in a zigzag fashionalong the first and second folding lines, and portions corresponding tothe first and second folding lines being bonded to the radially outerperipheral wall and the radially inner peripheral wall, respectively,thereby disposing the first and second heat-transfer plates radiately,defining the high-temperature fluid passage and the low-temperaturefluid passage alternately in the circumferential direction between theadjacent first and second heat-transfer plates, defining ahigh-temperature fluid passage inlet and a high-temperature fluidpassage outlet so as to open into axially opposite ends of thehigh-temperature fluid passage, and defining a low-temperature fluidpassage inlet and a low-temperature fluid passage outlet so as to openinto axially opposite ends of the low-temperature fluid passage,characterized in that the single folding plate blank is folded in thezigzag fashion over 360°, and opposite ends thereof are superposed oneon another and bonded together in an area including the first and secondfolding lines.

With the above arrangement, in forming the annular heat exchanger byfolding the folding plate blank including the first and secondheat-transfer plates which are alternately connected together throughthe first and second folding lines in the zigzag fashion, the singlefolding plate blank is folded in the zigzag fashion over 360°, and theopposite ends thereof are superposed one on another and bonded togetherin an area including the first or second folding line. Therefore, theheat exchanger can be formed by a minimum number of parts or components,and moreover, the number of bonded zones of the folding plate blank isthe minimum, one, thereby suppressing the possibility of leakage of thefluid to the minimum. In addition, the opposite ends of the foldingplate blank is merely cut and hence, it is unnecessary to conduct aspecial processing, leading to a reduced number of processing steps.Moreover, the folded portions of the folding plate blank including thefirst or second folding line are superposed one on another and hence,the bonding strength is increased. Further, the circumferential pitch ofthe adjacent first and second heat-transfer plates can be regulatedfinely only by changing the cutting positions of the folding plate blankto regulate the number of the first and second heat-transfer plates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 12 show a first embodiment of the present invention, wherein

FIG. 1 is a side view of the entire arrangement of a gas turbine engine;

FIG. 2 is a sectional view taken along a line 2—2 in FIG. 1;

FIG. 3 is an enlarged sectional view taken along a line 3—3 in FIG. 2 (asectional view of combustion gas passages);

FIG. 4 is an enlarged sectional view taken along a line 4—4 in FIG. 2 (asectional view of air passages);

FIG. 5 is an enlarged sectional view taken along a line 5—5 in FIG. 3;

FIG. 6 is an enlarged view of a portion indicated by 6 in FIG. 5;

FIG. 7 is an enlarged sectional view taken along a line 7—7 in FIG. 3;

FIG. 8 is a developed view of a folding plate blank;

FIG. 9 is a perspective view of an essential portion of the heatexchanger;

FIG. 10 is a pattern view showing flows of a combustion gas and air;

FIGS. 11A to 11C are graphs for explaining the operation when the pitchbetween projections is uniform;

FIGS. 12A to 12C are graphs for explaining the operation when the pitchbetween projections is non-uniform;

FIGS. 13 to 17 show a second embodiment of the present invention,wherein

FIG. 13 is a perspective view of the heat exchanger;

FIG. 14 is an enlarged sectional view taken along a line 14—14 in FIG.13 (a sectional view of combustion gas passages);

FIG. 15 is an enlarged sectional view taken along a line 15—15 in FIG.13 (a sectional view of air passages);

FIG. 16 is a sectional view taken along a line 16—16 in FIG. 14;

FIG. 17 is an enlarged sectional view taken along a line 17—17 in FIG.14;

FIGS. 18 to 21 show a modification to the first embodiment, wherein

FIG. 18 is a view similar to FIG. 8 showing the first embodiment, butaccording to the modification;

FIG. 19 is an enlarged view of an essential portion shown in FIG. 18;

FIG. 20 is a view taken in the direction of an arrow 20 in FIG. 19; and

FIG. 21 is a view similar to the FIG. 7 showing the first embodiment,but according to the modification.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will now be described withreference to FIGS. 1 to 12.

As shown in FIGS. 1 and 2, a gas turbine engine E includes an enginebody 1 in which a combustor, a compressor, a turbine and the like (whichare not shown) are accommodated. An annular heat exchanger 2 is disposedto surround an outer periphery of the engine body 1. Combustion gaspassages 4 and air passages 5 are circumferentially alternately providedin the heat exchanger 2 (see FIG. 5), so that a combustion gas of arelative high temperature passed through turbine is passed through thecombustion gas passages 4, and air of a relative low temperaturecompressed in the compressor is passed through the air passages 5. Asection in FIG. 1 corresponds to the combustion gas passages 4, and theair passages 5 are defined adjacent this side and on the other side ofthe combustion gas passages 4.

The sectional shape of the heat exchanger 2 taken along an axis isaxially longer and radially shorter flat hexagonal shape. A radiallyouter peripheral surface of the heat exchanger 2 is closed by alarger-diameter cylindrical outer casing 6, and a radially innerperipheral surface of the heat exchanger 2 is closed by asmaller-diameter cylindrical inner casing 7. A front end side (a leftside in FIG. 1) in the longitudinal section of the heat exchanger 2 iscut into an unequal-length angle shape, and an end plate 8 connected toan outer periphery of the engine body 1 is brazed to a portioncorresponding to an apex of the angle shape. A rear end side (a rightside in FIG. 1) in the section of the heat exchanger 2 is cut into anunequal-length angle shape, and an end plate 10 connected to an outerhousing 9 is brazed to a portion corresponding to an apex of the angleshape.

Each of the combustion gas passages 4 in the heat exchanger 2 includes acombustion gas passage inlet 11 and a combustion gas passage outlet 12at the left and upper portion and the right and lower portion of FIG. 1,respectively. A combustion gas introducing space (referred to as acombustion gas introducing duct) 13 defined along the outer periphery ofthe engine body 1 is connected at its downstream end to the combustiongas passage inlet 11. A combustion gas discharging space (referred to asa combustion gas discharging duct) 14 extending within the engine body 1is connected at its upstream end to the combustion gas passage outlet12.

Each of the air passages 5 in the heat exchanger 2 includes an airpassage inlet 15 and an air passage outlet 16 at the right and upperportion and the left and lower portion of FIG. 1, respectively. An airintroducing space (referred to as an air introducing duct) 17 definedalong an inner periphery of the outer housing 9 is connected at itsdownstream end to the air passage inlet 15. An air discharging space(referred to as an air discharging duct) 18 extending within the enginebody 1 is connected at its upstream end to the air passage outlet 16.

In this manner, the combustion gas and the air flow in oppositedirections from each other and cross each other as shown in FIGS. 3, 4and 10, whereby a counter flow and a so-called cross-flow are realizedwith a high heat-exchange efficiency. Thus, by allowing ahigh-temperature fluid and a low-temperature fluid to flow in oppositedirections from each other, a large difference in temperature betweenthe high-temperature fluid and the low-temperature fluid can bemaintained over the entire length of the flow paths, thereby enhancingthe heat-exchange efficiency.

The temperature of the combustion gas which has driven the turbine isabout 600 to 700° C. in the combustion gas passage inlets 11. Thecombustion gas is cooled down to about 300 to 400° C. in the combustiongas passage outlets 12 by conducting a heat-exchange between thecombustion gas and the air when the combustion gas passes through thecombustion,gas passages 4. On the other hand, the temperature of the aircompressed by the compressor is about 200 to 300° C. in the air passageinlets 15. The air is heated up to about 500 to 600° C. in the airpassage outlets 16 by conducting a heat-exchange between the air and thecombustion gas, which occurs when the air passes through the airpassages 5.

The structure of the heat exchanger 2 will be described below withreference to FIGS. 3 to 9.

As shown in FIGS. 3, 4 and 8, a body portion of the heat exchanger 2 ismade from a folding plate blank 21 produced by previously cutting a thinmetal plate such as a stainless steel into a predetermined shape andthen forming an irregularity on a surface of the cut plate by pressing.The folding plate blank 21 is comprised of first heat-transfer plates S1and second heat-transfer plates S2 disposed alternately, and is foldedinto a zigzag fashion along crest-folding lines L₁ and valley-foldinglines L₂. The term “crest-folding” means folding into a convex towardthis side or a closer side from the drawing sheet surface, and the term“valley-folding” means folding into a convex toward the other side or afar side from the drawing sheet surface. Each of the crest-folding linesL₁ and the valley-folding lines L₂ is not a simple straight line, butactually comprises an arcuate folding line for the purpose of forming apredetermined space between each of the first heat-transfer plates S1and each of the second heat-transfer plates S2.

A large number of first projections 22 and a large number of secondprojections 23, which are disposed at unequal distances, are formed oneach of the first and second heat-transfer plates S1 and S2 by pressing.The first projections 22 indicated by a mark X in FIG. 8 protrude towardthis side on the drawing sheet surface of FIG. 8, and the secondprojections 23 indicated by a mark O in FIG. 8 protrude toward the otherside on the drawing sheet surface of FIG. 8.

First projection stripes 24 _(F) and second projection stripes 25 _(F)are formed by pressing at those front and rear ends of the first andsecond heat-transfer plates S1 and S2 which are cut into the angleshape. The first projection stripes 24 _(F) protrude toward this side onthe drawing sheet surface of FIG. 8, and the second projection stripes25 _(F) protrude toward the other side on the drawing sheet surface ofFIG. 8. In any of the first and second heat-transfer plates S1 and S2, apair of the front and rear first projection stripes 24 _(F), 24 _(R) aredisposed at diagonal positions, and a pair of the front and rear secondprojection stripes 25 _(F), 25 _(R) are disposed at other diagonalpositions.

The first projections 22, the second projections 23, the firstprojection stripes 24 _(F), 24 _(R) and the second projection stripes 25_(F), 25 _(R) of the first heat-transfer plate S1 shown in FIG. 3 are inan opposite recess-projection relationship with respect to that in thefirst heat-transfer plate S1 shown in FIG. 8. This is because FIG. 3shows a state in which the first heat-transfer plate S1 is viewed fromthe back side.

As can be seen from FIGS. 5 and 8, when the first and secondheat-transfer plates Si and S2 of the folding plate blank 21 are foldedalong the crest-folding lines L₁ to form the combustion gas passages 4between both the heat-transfer plates S1 and S2, tip ends of the secondprojections 23 of the first heat-transfer plate S1 and tip ends of thesecond projections 23 of the second heat-transfer plate S2 are broughtinto abutment against each other and brazed to each other. In addition,the second projection stripes 25 _(F), 25 _(R) of the firstheat-transfer plate S1 and the second projection stripes 25 _(F), 25_(R) of the second heat-transfer plate S2 are brought into abutmentagainst each other and brazed to each other. Thus, a left lower portionand a right upper portion of the combustion gas passage 4 shown in FIG.3 are closed, and each of the first projection stripes 24 _(F), 24 _(R)of the first heat-transfer plate S1 and each of the first projectionstripes 24 _(F), 24 _(R) of the second heat-transfer plate S2 areopposed to each other with a gap left therebetween. Further, thecombustion gas passage inlet 11 and the combustion gas passage outlet 12are defined in a left, upper portion and a right, lower portion of thecombustion gas passage 4 shown in FIG. 3, respectively.

When the first heat-transfer plates S1 and the second heat-transferplates S2 of the folding plate blank 21 are folded along thevalley-folding line L₂ to form the air passages 5 between both theheat-transfer plates S1 and S2, the tip ends of the first projections 22of the first heat-transfer plate S1 and the tip ends of the firstprojections 22 of the second heat-transfer plate S2 are brought intoabutment against each other and brazed to each other. In addition, thefirst projection stripes 24 _(F), 24 _(R) of the first heat-transferplate S1 and the first projection stripes 24 _(F), 24 _(R) of the secondheat-transfer plate S2 are brought into abutment against each other andbrazed to each other. Thus, a left upper portion and a right lowerportion of the air passage 5 shown in FIG. 4 are closed, and each of thesecond projection stripes 25 _(F), 25 _(R) of the first heat-transferplate S1 and each of the second projection stripes 25 _(F), 25 _(R) ofthe second heat-transfer plate S2 are opposed to each other with a gapleft therebetween. Further, the air passage inlet 15 and the air passageoutlet 16 are defined at a right upper portion and a left lower portionof the air passage 5 shown in FIG. 4, respectively.

Each of the first and second projections 22 and 23 has a substantiallytruncated conical shape, and the tip ends of the first and secondprojections 22 and 23 are in surface contact with each other to enhancethe brazing strength. Each of the first and second projection stripes 24_(F), 24 _(R and 25) _(F), 25 _(R) has also a substantially trapezoidalsection, and the tip ends of the first and second projection stripes 24_(F), 24 _(R) and 25 _(F), 25 _(R) are also in surface contact with eachother to enhance the brazing strength.

As can be seen from FIG. 5, radially inner peripheral portions of theair passages 5 are automatically closed, because they correspond to thefolded portion (the valley-folding line L₂) of the folding plate blank21, but radially outer peripheral portions of the air passages 5 areopened, and such opening portions are closed by brazing to the outercasing 6. On the other hand, radially outer peripheral portions of thecombustion gas passages 4 are automatically closed, because theycorrespond to the folded portion (the crest-folding line L₁) of thefolding plate blank 21, but radially inner peripheral portions of thecombustion gas passages 4 are opened, and such opening portions areclosed by brazing to the inner casing 7.

When the folding plate blank 21 is folded in the zigzag fashion, theadjacent crest-folding lines L₁ cannot be brought into direct contactwith each other, but the distance between the crest-folding lines L₁ ismaintained constant by the contact of the first projections 22 to eachother. In addition, the adjacent valley-folding lines L₂ cannot bebrought into direct contact with each other, but the distance betweenthe valley-folding lines L₂ is maintained constant by the contact of thesecond projections 23 to each other.

When the folding plate blank 21 is folded in the zigzag fashion toproduce the body portion of the heat exchanger 2, the first and secondheat-transfer plates S1 and S2 are disposed radiately from the center ofthe heat exchanger 2. Therefore, the distance between the adjacent firstand second heat-transfer plates S1 and S2 assumes the maximum in theradially outer peripheral portion which is in contact with the outercasing 6, and the minimum in the radially inner peripheral portion whichis in contact with the inner casing 7. For this reason, the heights ofthe first projections 22, the second projections 23, the firstprojection stripes 24 _(F), 24 _(R) and the second projection stripes 25_(F), 25 _(R) are gradually increased outwards from the radially innerside, whereby the first and second heat-transfer plates S1 and S2 can bedisposed exactly radiately (see FIG. 5).

By employing the above-described structure of the radiately foldedplates, the outer casing 6 and the inner casing 7 can be positionedconcentrically, and the axial symmetry of the heat exchanger 2 can bemaintained accurately.

As can be seen from FIGS. 7 and 9, rectangular small piece-shaped flangeportions 26 are formed by folding, apexes of front and rear ends of thefirst and second heat-transfer plates S1 and S2 cut into the angleshape, at an angle slightly smaller than 90° in the circumferentialdirection of the heat exchanger 2. When the folding plate blank 21 isfolded in the zigzag fashion, a portion of each of the flanges 26 of thefirst and second heat-transfer plates S1 and S2 is superposed on andbrazed in a surface contact state to a portion of the adjacent flangeportion 26, thereby forming an annular bonding flange 27 as a whole. Thebonding flange 27 is bonded by brazing to the front and rear end plates8 and 10.

At this time, the front surface of the bonding flange 27 is of a steppedconfiguration, and a slight gap is defined between the bonding flange 27and each of the end plates 8 and 10, but the gap is closed by a brazingmaterial (see FIG. 7). The flange portions 26 are folded in the vicinityof the tip ends of the first projection stripes 24 _(F) and 24 _(R) andthe second projection stripes 25 _(F) and 25 _(R) formed on the firstand second heat-transfer plates S1 and S2. When the folding plate blank21 has been folded along the crest-folding line L₁ and thevalley-folding line L₂, slight gaps are also defined between the tipends of the first projection stripes 24 _(F) and 24 _(R) and the secondprojection stripes 25 _(F) and 25 _(R) and the flange portions 26, butthe gaps are closed by the brazing material (see FIG. 7).

If an attempt is made to cut the apex portions of angle shapes of thefirst and second heat-transfer plates S1 and S2 into flat, and braze theend plates 8 and 10 to end surfaces resulting from such cutting, it isnecessary to first fold the folding plate blank 21 and braze the firstprojections 22 and the second projections 23 as well as the firstprojection stripes 24 _(F) and 24 _(R) and the second projection stripes25 _(F) and 25 _(R) of the first and second heat-transfer plates S1 andS2 to each other, and then subject the apex portions to a precisecutting treatment for brazing to the end plates 8 and 10. In this case,the two brazing steps are required, resulting in not only an increasednumber of steps but also an increased cost because of a high processingprecision required for the cut surfaces. Moreover, it is difficult toprovide a strength sufficient for brazing of the cut surfaces having asmall area. However, by brazing the flange portions 26 formed by thefolding, the brazing of the first projections 22 and the secondprojections 23 as well as the first projection stripes 24 _(F) and 24_(R) and the second projection stripes 25 _(F) and 25 _(R) and thebrazing of the flange portions 26 can be accomplished in a continuousflow, and further, the precise cutting treatment of the apex portions ofthe angle shapes is not required. Moreover, the flange portions 26 insurface contact with one another are brazed together, leading toremarkably increased brazing strength. Further, the flange portionsthemselves form the bonding flange 27, which can contribute to areduction in number of parts.

By folding the folding plate blank 21 radiately and in the zigzagfashion to form the first and second heat-transfer plates S1 and S2continuously, the number of parts and the number of points to be brazedcan be reduced remarkably, and moreover, the dimensional precision ofthe completed article can be enhanced, as compared with the case where alarge number of first heat-transfer plates S1 individually independentfrom one another and a large number of second heat-transfer plates S2individually independent from one another are brazed alternately.

As can be seen from FIGS. 5 and 6, when the single folding plate blank21 formed into a band shape is folded in a zigzag fashion to form thebody portion of the heat exchanger 2, opposite ends of the folding plateblank 21 are integrally bonded to each other at a radially outerperipheral portion of the heat exchanger 2. Therefore, end edges of thefirst and second heat-transfer plates S1 and S2 adjoining each otherwith the bonded portion interposed therebetween are cut into a J-shapein the vicinity of the crest-folding line L₁, and for example, an outerperiphery of the J-shaped cut portion of the second heat-transfer plateS2 is fitted to and brazed to an inner periphery of the J-shaped cutportion of the first heat-transfer plate S1. Since the J-shaped cutportions of the first and second heat-transfer plates S1 and S2 arefitted to each other, the J-shaped cut portion of the outer firstheat-transfer plate S1 is forced to be expanded, while the J-shaped cutportion of the inner second heat-transfer plate S2 is forced to becontracted. Further, the inner second heat-transfer plate S2 iscompressed inwards radially of the heat exchanger 2.

By employing the above-described structure, a special bonding member forbonding the opposite ends of the folding plate blank 21 to each other isnot required, and a special processing such as changing the shape of thefolding plate blank 21 is not required, either. Therefore, the number ofparts and the processing cost are reduced, and an increase in heat massin the bonded zone is avoided. Moreover, a dead space which is not thecombustion gas passages 4 nor the air passages 5 is not created andhence, the increase in flow path resistance is maintained to theminimum, and there is not a possibility that the heat exchangeefficiency may be reduced. Further, the bonded zone of the J-shaped cutportions of the first and second heat-transfer plates S1 and S2 isdeformed and hence, a very small gap is liable to be produced. However,only the bonded zone may be the minimum, one by forming the body portionof the heat exchanger 2 by the single folding plate blank 21, and theleakage of the fluid can be suppressed to the minimum. Additionally,when the single folding plate blank 21 is folded in the zigzag fashionto form the body portion of the annular heat exchanger 2, if the numbersof the first and second heat-transfer plates S1 and S2 integrallyconnected to each other are not suitable, the circumferential pitchbetween the adjacent first and second heat-transfer plates S1 and S2 isinappropriate and moreover, there is a possibility that the tip ends ofthe first and second projection 22 and 23 may be separated or crushed.However, the circumferential pitch can be finely regulated easily onlyby changing the cutting position of the folding plate blank 21 toproperly change the numbers of the first and second heat-transfer platesS1 and S2 integrally connected to each other.

During operation of the gas turbine engine E, the pressure in thecombustion gas passages 4 is relatively low, and the pressure in the airpassages 5 is relatively high. For this reason, a flexural load isapplied to the first and second heat-transfer plates S1 and S2 due to adifference between the pressures, but a sufficient rigidity capable ofwithstanding such load can be obtained by virtue of the first and secondprojections 22 and 23 which have been brought into abutment against eachother and brazed with each other.

In addition, the surface areas of the first and second heat-transferplates S1 and S2 (i.e., the surface areas of the combustion gas passages4 and the air passages 5) are increased by virtue of the first andsecond projections 22 and 23. Moreover, the flows of the combustion gasand the air are agitated and hence, the heat exchange efficiency can beenhanced.

The unit amount N_(tu) of heat transfer representing the amount of heattransferred between the combustion gas passages 4 and the air passages 5is given by the following equation (1):

 N _(tu)=(K×A)/[C×(dm/dt)]  (1)

In the above equation (1), K is an overall heat transfer coefficient ofthe first and second heat-transfer plates S1 and S2; A is an area (aheat-transfer area) of the first and second heat-transfer plates S1 andS2; C is a specific heat of a fluid; and dm/dt is a mass flow rate ofthe fluid flowing in the heat transfer area. Each of the heat transferarea A and the specific heat C is a constant, but each of the overallheat transfer coefficient K and the mass flow rate dm/dt is a functionof a pitch P (see FIG. 5) between the adjacent first projections 22 orbetween the adjacent second projections 23.

When the unit amount N_(tu) of heat transfer is varied in the radialdirections of the first and second heat-transfer plates S1 and S2, thedistribution of temperature of the first and second heat-transfer platesS1 and S2 is non-uniformed radially, resulting in a reduced heatexchange efficiency, and moreover, the first and second heat-transferplates S1 and S2 are non-uniformly, thermally expanded radially togenerate undesirable thermal stress. Therefore, if the pitch P of radialarrangement of the first and second projections 22 and 23 is setsuitably, so that the unit amount N_(tu) of heat transfer is constant inradially various sites of the first and second heat-transfer plates S1and S2, the above problems can be overcome.

When the pitch P is set constant in the radial directions of the heatexchanger 2, as shown in FIG. 11A, the unit amount N_(tu) of heattransfer is larger at the radially inner portion and smaller at theradially outer portion, as shown in FIG. 11B. Therefore, thedistribution of temperature of the first and second heat-transfer platesS1 and S2 is also higher at the radially inner portion and lower at theradially outer portion, as shown in FIG. 11C. On the other hand, if thepitch P is set so that it is larger in the radially inner portion of theheat exchanger 2 and smaller in the radially outer portion of the heatexchanger 2, as shown in FIG. 12A, the unit amount N_(tu) of heattransfer and the distribution of temperature can be made substantiallyconstant in the radial directions, as shown in FIGS. 12B and 12C.

As can be seen from FIGS. 3 to 5, in the heat exchanger 2 according tothis embodiment, a region R₁ having a small pitch P of radialarrangement of the first and second projections 22 and 23 is provided inthe radially outer portions of the axially intermediate portions of thefirst and second heat-transfer plates S1 and S2 (namely, portions otherthan the angle-shaped portions at the axially opposite ends), and aregion R₂ having a large pitch P of radial arrangement of the first andsecond projections 22 and 23 is provided in the radially inner portion.Thus, the unit number N_(tu) of heat transfer can be made substantiallyconstant over the entire region of the axially intermediate portions ofthe first and second heat-transfer plates S1 and S2, and it is possibleto enhance the heat exchange efficiency and to alleviate the thermalstress.

If the entire shape of the heat exchanger and the shapes of the firstand second projections 22 and 23 are varied, the overall heat transfercoefficient K and the mass flow rate dm/dt are also varied and hence,the suitable arrangement of pitches P is also different from that in thepresent embodiment. Therefore, in addition to a case where the pitch Pis gradually decreased radially outwards as in the present embodiment,the pitch P may be gradually increased radially outwards in some cases.However, if the arrangement of pitches P is determined such that theabove-described equation (1) is established, the operational effect canbe obtained irrespective of the entire shape of the heat exchanger andthe shapes of the first and second projections 22 and 23.

As can be seen from FIGS .3 and 4, in the axially intermediate portionsof the first and second heat-transfer plates S1 and S2, the adjacentfirst projections 22 or the adjacent second projections 23 are notarranged in a row in the axial direction of the heat exchanger 2 (in thedirection of flowing of the combustion gas and the air), but arearranged so as to be inclined at a predetermined angle with respect tothe axial direction. In other words, a consideration is taken so thatthe first projections 22 as well as the second projections 23 cannot bearranged continuously on a straight line parallel to the axis of theheat exchanger 2. Thus, the combustion gas passages 4 and the airpassages 5 can be defined in a labyrinth-shaped configuration by thefirst and second projections 22 and 23 in the axially intermediateportions of the first and second heat-transfer plates S1 and S2, therebyenhancing the heat exchange efficiency.

Further, the first and second projections 22 and 23 are arranged in theangle-shaped portions at the axially opposite ends of the first andsecond heat-transfer plates S1 and S2 at an arrangement pitch differentfrom that in the axially intermediate portion. In the combustion gaspassage 4 shown in FIG. 3, the combustion gas flowing thereinto throughthe combustion gas passage inlet 11 in the direction of an arrow a isturned in the axial direction to flow in the direction of an arrow b,and is further turned in the direction of an arrow c to flow out throughthe combustion gas passage outlet 12. When the combustion gas changesits course in the vicinity of the combustion gas passage inlet 11, acombustion gas flow path P_(s) is shortened on the inner side as viewedin the turning direction (on the radially outer side of the heatexchanger 2), and a combustion gas flow path P_(L) is prolonged on theouter side as viewed in the turning direction (on the radially innerside of the heat exchanger 2). On the other hand, when the combustiongas changes its course in the vicinity of the combustion gas passageoutlet 12, the combustion gas flow path P_(S) is shortened on the innerside as viewed in the turning direction (on the radially inner side ofthe heat exchanger 2), and the combustion gas flow path P_(L) isprolonged on the outer side as viewed in the turning direction (on theradially outer side of the heat exchanger 2). When a difference isproduced between the lengths of the combustion gas flow paths on theinner and outer sides as viewed in the direction of turning of thecombustion gas, the combustion gas flows in a drifting manner from theouter side as viewed in the turning direction toward the inner sidewhere the flow resistance is small because of the short flow path,whereby the flow of the combustion gas is non-uniformized, resulting ina reduction in heat exchange efficiency.

Therefore, in regions R₃, R₃ in the vicinity of the combustion gaspassage inlet 11 and the combustion gas passage outlet 12, the pitch ofarrangement of the first projections 22 as well as the secondprojections 23 in the direction perpendicular to the direction offlowing of the combustion gas is varied so that it becomes graduallydenser from the outer side toward the inner side as viewed in theturning direction. By non-uniformizing the pitch of arrangement of thefirst projections 22 as well as the second projections 23 in the regionsR₃, R₃ in the above manner, the first and second projections 22 and 23can be arranged densely on the inner side as viewed in the turningdirection where the flow path resistance is small because of the shortflow path of the combustion gas, whereby the flow path resistance can beincreased, thereby uniformizing the flow path resistance over the entireregions R₃, R₃. Thus, the generation of the drifting flow can beprevented to avoid the reduction in heat exchange efficiency.Particularly, all the projections in a first row adjacent the inner sideof the first projection stripes 24 _(F), 24 _(R) comprise the secondprojections 23 protruding into the combustion gas passages 4 (indicatedby a mark x in FIG. 3). Therefore, a drifting flow preventing effect caneffectively be exhibited by non-uniformizing the pitch of arrangement ofthe second projections 23.

Likewise, in the air passage 5 shown in FIG. 4, the air flowingthereinto in the direction of an arrow d through the air passage inlet15 is turned axially to flow in the direction of an arrow e, and furtherturned in the direction of an arrow f to flow out through the airpassage outlet 16. When the air changes its course in the vicinity ofthe air passage inlet 15, the air flow path is shortened on the innerside as viewed in the turning direction (on the radially outer side ofthe heat exchanger 2), and the air flow path is prolonged on the outerside as viewed in the turning direction (on the radially inner side ofthe heat exchanger 2). On the other hand, when the air changes itscourse in the vicinity of the air passage outlet 16, the air flow pathis shortened on the inner side as viewed in the turning direction (onthe radially inner side of the heat exchanger 2), and the air flow pathis prolonged on the outer side as viewed in the turning direction (onthe radially outer side of the heat exchanger 2). When a difference isgenerated between the lengths of the air flow paths on the inner andouter sides as viewed in the direction of turning of the air, the airflows in a drifting manner toward the inner side as viewed in theturning direction where the flow path resistance is smaller because ofthe short flow path, thereby reducing the heat exchange efficiency.

Therefore, in regions R₄, R₄ in the vicinity of the air passage inlet 15and the air passage outlet 16, the pitch of arrangement of the firstprojections 22 as well as the second projections 23 in the directionperpendicular to the direction of flowing of the air is varied so thatit becomes gradually denser from the outer side toward the inner side asviewed in the turning direction. By non-uniformizing the pitch ofarrangement of the first projections 22 as well as the secondprojections 23 in the regions R₄, R₄ in the above manner, the first andsecond projections 22 and 23 can be arranged densely on the inner sideas viewed in the turning direction where the flow path resistance issmall because of the short flow path of the air, whereby the flow pathresistance can be increased, thereby uniformizing the flow pathresistance over the entire regions R₄, R₄. Thus, the generation of thedrifting flow can be prevented to avoid the reduction in heat exchangeefficiency. Particularly, all the projections in a first row adjacentthe inner side of the second projection stripes 25 _(F), 25 _(R)comprise the first projections 22 protruding into the combustion gaspassages 4 (indicated by a mark x in FIG. 4). Therefore, a drifting flowpreventing effect can effectively be exhibited by non-uniformizing thepitch of arrangement of the first projections 22.

When the combustion gas flows in each of the regions R₄, R₄ adjacent theregions R₃, R₃ in FIG. 3, the pitch of arrangement of the firstprojections 22 as well as the second projections 23 in the region R₄, R₄little exerts an influence to the flowing of the combustion gas, becausethe pitch is non-uniform in the direction of flowing of the combustiongas. Likewise, when the air flows in each of the regions R₃, R₃ adjacentthe regions R₄, R₄ in FIG. 4, the pitch of arrangement of the firstprojections 22 as well as the second projections 23 in the region R₃, R₃little exerts an influence to the flowing of the combustion gas, becausethe pitch is non-uniform in the direction of flowing of the air.

As can be seen from FIGS. 3 and 4, the first and second heat-transferplates S1 and S2 are cut into an unequal-length angle shape having along side and a short side at the front and rear ends of the heatexchanger 2. The combustion gas passage inlet 11 and the combustion gaspassage outlet 12 are defined along the long sides at the front and rearends, respectively, and the air passage inlet 15 and the air passageoutlet 16 are defined along the short sides at the rear and front ends,respectively.

In this way, the combustion gas passage inlet 11 and the air passageoutlet 16 are defined respectively along the two sides of the angleshape at the front end of the heat exchanger 2, and the combustion gaspassage outlet 12 and the air passage inlet 15 are defined respectivelyalong the two sides of the angle shape at the rear end of the heatexchanger 2. Therefore, larger sectional areas of the flow paths in theinlets 11, 15 and the outlets 12, 16 can be ensured to suppress thepressure loss to the minimum, as compared with a case where the inlets11, 15 and the outlets 12, 16 are defined without cutting of the frontand rear ends of the heat exchanger 2 into the angle shape. Moreover,since the inlets 11, 15 and the outlets 12, 16 are defined along the twosides of the angle shape, not only the flow paths for the combustion gasand the air flowing out of and into the combustion gas passages 4 andthe air passages 5 can be smoothened to further reduce the pressureloss, but also the ducts connected to the inlets 11, 15 and the outlets12, 16 can be disposed in the axial direction without sharp bending ofthe flow paths, whereby the radial dimension of the heat exchanger 2 canbe reduced.

As compared with the volume flow rate of the air passed through the airpassage inlet 15 and the air passage outlet 16, the volume flow rate ofthe combustion gas, which has been produced by burning a fuel-airmixture resulting from mixing of fuel into the air and expanded in theturbine into a dropped pressure, is larger. In the present embodiment,the unequal-length angle shape is such that the lengths of the airpassage inlet 15 and the air passage outlet 16, through which the air ispassed at the small volume flow rate, are short, and the lengths of thecombustion gas passage inlet 11 and the combustion gas passage outlet12, through which the combustion gas is passed at the large volume flowrate, are long. Thus, it is possible to relatively reduce the flow rateof the combustion gas to more effectively avoid the generation of apressure loss.

As can be seen from FIGS. 3 and 4, the outer housing 9 made of stainlesssteel is of a double structure comprised of outer wall members 28 and 29and inner wall members 30 and 31 to define the air introducing duct 17.A front flange 32 bonded to rear ends of the front outer and inner wallmembers 28 and 30 is coupled to a rear flange 33 bonded to front ends ofthe rear outer and inner wall members 29 and 31 by a plurality of bolts34. At this time, an annular seal member 35 which is E-shaped in sectionis clamped between the front and rear flanges 32 and 33 to seal thecoupled surfaces of the front and rear flanges 32 and 33, therebypreventing the air within the air introducing duct 17 from being mixedwith the combustion gas within the combustion gas introducing duct 13.

The heat exchanger 2 is supported on the inner wall member 31 connectedto the rear flange 33 of the outer housing 9 through a heat exchangersupporting ring 36 made of the same plate material under the trade nameof “Inconel” as the heat exchanger 2. The inner wall member 31 bonded tothe rear flange 33 can be considered substantially as a portion of therear flange 33, because of its small axial dimension. Therefore, theheat exchanger supporting ring 36 can be bonded directly to the rearflange 33 in place of being bonded to the inner wall member 31. The heatexchanger supporting ring 36 is formed into a stepped shape in sectionand includes a first ring portion 36 ₁ bonded to the outer peripheralsurface of the heat exchanger 2, a second ring portion 36 ₂ bonded tothe inner peripheral surface of the inner wall member 31 and having adiameter larger than that of the first ring portion 36 ₁, and aconnecting portion 36 ₃ which connects the first and second ringportions 36 ₁ and 36 ₂ to each other in an oblique direction. Thecombustion gas passage inlet 11 and the air passage inlet 15 are sealedfrom each other by the heat exchanger supporting ring 36.

The profile of temperature on the outer peripheral surface of the heatexchanger 2 is such that the temperature is lower on the side of the airpassage inlet 15 (on the axially rear side) and higher on the side ofthe combustion gas passage inlet 11 (on the axially front side). Bymounting the heat exchanger supporting ring 36 at a location closer tothe air passage inlet 15 than to the combustion gas passage inlet 11,the difference between the amounts of thermal expansion of the heatexchanger 2 and the outer housing 9 can be maintained to the minimum todecrease the thermal stress. When the heat exchanger 2 and the rearflange 33 are displaced relative to each other due to the differencebetween the amounts of thermal expansion, such displacement can beabsorbed by the resilient deformation of the heat exchanger supportingring 36 made of plate material, thereby alleviating the thermal stressacting on the heat exchanger 2 and the outer housing 9. Particularly,since the section of the heat exchanger supporting ring 36 is formed inthe stepped configuration, the folded portions thereof can easily bedeformed to effectively absorb the difference between the amounts ofthermal expansion.

A second embodiment of the present invention will now be described withreference to FIGS. 13 to 17.

A heat exchanger 2 is formed into a rectangular parallelepiped shape asa whole and surrounded by an upper bottom wall 41 and a lower bottomwall 42, a front end wall 43 and a rear end wall 44, and a left sidewall45 and a right sidewall 46. The combustion gas passage inlet 11 and thecombustion gas passage outlet 12 extending laterally open into front andrear portions of the upper bottom wall 41, respectively, and the airpassage inlet 15 and the air passage outlet 16 extending laterally openinto rear and front portions of the lower bottom wall 42, respectively.The first rectangular heat-transfer plates S1 and the second rectangularheat-transfer plates S2 are alternately disposed within the heatexchanger 2 and formed by folding the folding plate blank 21 in a zigzagfashion along the crest-folding lines L₁ and the valley-folding linesL₂.

The combustion gas passages 4 connected to the combustion gas passageinlet and outlet 11 and 12 and the air passages 5 connected to the airpassage inlet and outlet 15 and 16 are alternately defined between thefirst and second heat-transfer plates S1 and S2. At this time, thedistances between the first and second heat-transfer plates S1 and S2are maintained constant by brazing a plurality of first projections 22and a plurality of second projections 23 formed on the first and secondheat-transfer plates S1 and S2 at their tip ends to each other.

The folding plate blank 21 is brazed to the upper bottom wall 41 at thecrest-folding lines L₁ and to the lower bottom wall 42 at thevalley-folding lines L₂. Shorter portions (i.e., front and rear ends) ofthe first and second heat-transfer plates S1 and S2 are folded throughan angle slightly smaller than 90° to form the rectangular flangeportions 26. The flange portions 26 are superposed one on another andbrazed to one another in surface contact to form the bonding flange 27rectangular as a whole. The bonding flange 27 is bonded to each of thefront end wall 43 and the rear end wall 44 by brazing. A gap between thebonding flange 27 and each of the front and rear end walls 43 and 44 isclosed by a brazing material (see FIG. 17). By brazing the flangeportions 26 formed by folding the ends of the first and secondheat-transfer plates S1 and S2 to one another in the above manner, aprecise cutting treatment of the ends of the first and secondheat-transfer plates S1 and S2 is not required. Therefore, the brazingof the first and second projections 22 and 23 and the brazing of theflange portions 26 can be accomplished in a continuous flow, andmoreover, because the flange portions 26 in surface contact with oneanother are brazed together, the brazing strength is increasedremarkably.

As shown in FIGS. 14 and 15, the arrangement of the first projections 22and the second projections 23 formed in the first heat-transfer platesS1 and the second heat-transfer plates S2 is different between thelongitudinally intermediate portion and the longitudinally opposite endportions (the areas facing the combustion gas passage inlet 11 and theair passage outlet 16 as well as the areas facing the combustion gaspassage outlet 12 and the air passage inlet 15) of the firstheat-transfer plates S1 and the second heat-transfer plates S2.

More specifically, the first and second projections 22 and 23 arearranged vertically at equal pitches and longitudinally at equal pitchesin the longitudinally intermediate portions of the first and secondheat-transfer plates S1 and S2. On the other hand, the first and thesecond projections 22 and 23 are arranged vertically at equal pitches inthe longitudinally opposite end portions, but longitudinally at unequalpitches. Specifically, the pitch of longitudinal arrangement of thefirst and second projections 22 and 23 is denser at a location fartherfrom the front ends in the areas facing the combustion gas passage inlet11 and the air passage outlet 16, and denser at a location farther fromthe rear ends in the areas facing the combustion gas passage outlet 12and the air passage inlet 15.

Therefore, when the combustion gas flowing into the heat exchangerthrough the combustion gas passage inlet 11 in the direction of an arrowg in FIG. 14 is turned at 90° in the direction along the combustion gaspassages 4, the flow path resistance in the inner passage as viewed inthe turning direction, where the combustion gas is easy to flow becauseof the short flow path, can be increased by the first and secondprojections 22 and 23 arranged in the denser relation, therebyuniformizing the flow rate of the combustion gas on the inner and outersides as viewed in the turning direction. When the combustion gasflowing in the direction along the combustion gas passages 4 is turnedat 90° to flow out through the combustion gas passage outlet 12 in thedirection of an arrow h, the flow path resistance in the inner passageas viewed in the turning direction, where the combustion gas is easy toflow because of the shorter flow path, can be increased by the first andsecond projections 22 and 23 arranged in the denser relation, therebyuniformizing the flow rate of the combustion gas on the inner and outersides as viewed in the turning direction.

Likewise, the air flowing into the heat exchanger through the airpassage inlet 15 in the direction of an arrow i in FIG. 15 is turned at90° in the direction along the air passages 5, the flow path resistancein the inner passage as viewed in the turning direction, where the airis easy to flow because of the short flow path, can be increased by thefirst and second projections 22 and 23 arranged in the denser relation,thereby uniformizing the flow rate of the combustion gas on the innerand outer sides as viewed in the turning direction. When the air flowingin the direction along the air passages 5 is turned at 90° to flow outthrough the air passage outlet 16 in the direction of an arrow j, theflow path resistance in the inner passage as viewed in the turningdirection, where the air is easy to flow because of the shorter flowpath, can be increased by the first and second projections 22 and 23arranged in the denser relation, thereby uniformizing the flow rate ofthe air on the inner and outer sides as viewed in the turning direction.

A modification to the above-described first embodiment will now bedescribed with reference to FIGS. 18 to 21.

As shown in FIG. 18, in the first and second heat-transfer plates S1 andS2 of the folding plate blank 21, the shape of the flange portion 26 atan apex of an angle shape is slightly different from that in the firstembodiment. FIGS. 19 and 20 show the shape of the flange portion 26 ofthe first heat-transfer plate S1. The flange portion 26 is comprised ofa folded portion 26 ₁ in which the height of the first projection stripe24 _(F) as well as the second projection stripe 25 _(F) is graduallydecreased, and a flat portion 26 ₂ connected to a tip end of the foldedportion 26 ₁. The length of the flat portion 26 ₂ is long in the firstheat-transfer plate S1 and shorter in the second heat-transfer plate S2(see FIG. 18).

Thus, as can be seen from FIG. 21, each of the flange portions 26 of thefirst and second heat-transfer plates S1 and S2 is folded into anarcuate shape over 90° in a section of the folded portion 26 ₁, and theflat portion 26 ₂ is brazed in surface contact to the end plate 8. Atthis time, when the fist projection stripes 24 _(F) or the secondprojection stripes 25 _(F) are brazed to one another, the gaptherebetween can be maintained to the minimum, because the height of thefirst and second projection stripes 24 _(F) and 25 _(F) is graduallydecreased at the folded portion 26 ₁. Moreover, the length of the flatportion 26 ₂ of the flange portion 26 of the second heat-transfer plateS2 is short and hence, the tip end of the flat portion 26 ₂ cannotinterfere with the first and second projection stripes 24 _(F) and 25_(F) of the adjacent first heat-transfer plate S1, whereby thegeneration of the gap is further effectively prevented. The flangeportions 26 on one side of the first and second heat-transfer plates S1and S2 are shown in FIGS. 19 to 21, but the flange portions 26 on theother side are of the same structure as those on the one side.

According to such modification, the gap produced between the abutmentsof the first projection stripes 24 _(F) as well as between the abutmentsof the second projection stripes 25 _(F) can be maintained to theminimum, thereby enhancing the sealability to the fluid.

Although the embodiments of the present invention have been described indetail, it will be understood that the present invention is not limitedto the above-described embodiments, and various modifications may bemade without departing from the spirit and scope of the inventiondefined in claims.

For example, in the invention according to claims 1 to 11, the first andsecond heat-transfer plates S1 and S2 may be formed from differentmaterials and bonded to each other, in place of use of the folding plateblank 21. In the invention according to claim 12, the opposite ends ofthe folding plate blank 21 may be bonded to each other at a locationcorresponding to the second folding line L₂, in place of being bonded toeach other at the location corresponding to the first folding line

What is claimed is:
 1. A heat exchanger, comprising a plurality of firstheat-transfer plates (S1) and a plurality of second heat-transfer plates(S2) disposed radiately in an annular space defined between a radiallyouter peripheral wall (6) and a radially inner peripheral wall (7), anda high-temperature fluid passage (4) and a low-temperature fluid passage(5) which are defined circumferentially alternately between adjacentones of said first and second heat-transfer plates (S1 and S2) bybonding pluralities of projections (22 and 23) formed on said first andsecond heat-transfer plates (S1 and S2) to one another, axially oppositeends of each of said first and second heat-transfer plates (S1 and S2)being cut into angle shapes each having two end edges with an apexportion disposed between and projecting from the two end edges, therebydefining a high-temperature fluid passage inlet (11) by closing one ofsaid two end edges and opening the other end edge at axially one end ofsaid high-temperature fluid passage (4), and defining a high-temperaturefluid passage outlet (12) by closing one of said two end edges andopening the other end edge at the axially other end of saidhigh-temperature fluid passage (4), defining a low-temperature fluidpassage outlet (16) by opening one of said two end edges and closing theother end edge at axially one end of said low-temperature fluid passage(5), and defining a low-temperature fluid passage inlet (15) by openingone of said two end edges and closing the other end edge at the axiallyother end of said low-temperature fluid passage (5), each of the firstand second heat-transfer plates having a first flange portion and asecond flange portion disposed opposite the first flange portion, eachof the first and second flange portions being respective folded ones ofthe apex portions of the angle shape, respective first and secondflanges sized and folded to be superposed one on another and bondedtogether, wherein said high-temperature fluid passage inlet (11) andsaid low-temperature fluid passage outlet (16) are partitioned from eachother in fluidic isolation by said superposed first flange portions (26)being disposed therebetween and wherein said high-temperature fluidpassage outlet (12) and said low-temperature fluid passage inlet (15)are partitioned from each other in fluidic isolation by the superposedsecond flange portions (26 disposed therebetween.
 2. A heat exchangeraccording to claim 1, characterized in that a folding plate blank (21)including said first and second heat-transfer plates (S1 and S2) whichare alternately connected together through first and second foldinglines (L₁ and L₂) is folded in a zigzag fashion along said first andsecond folding lines (L₁ and L₂), and portions corresponding to saidfirst folding lines (L₁) are bonded to said radially outer peripheralwall (6), while portions corresponding to said second folding lines (L₂)are bonded to said radially inner peripheral wall (7).
 3. A heatexchanger according to claim 1, characterized in that said flangeportions (26) are folded into an arcuate shape and superposed one onanother, and a height of projection stripes (24 _(F), 24 _(R), 25 _(F)and 25 _(R)) formed along angle-shaped end edges of said first andsecond heat-transfer plates (S1 and S2) is gradually decreased in saidflange portions (26) in order to close said fluid passage inlets andoutlets (11, 12, 15 and 16).
 4. A heat exchanger, comprising a pluralityof first heat-transfer plates and a plurality of second heat-transferplates which are disposed radiately in an annular space defined betweena radially outer peripheral wall and a radially inner peripheral wall,wherein a high-temperature fluid passage and a low-temperature fluidpassage are defined alternately in a circumferential direction betweenadjacent ones of said first and second heat-transfer plates, axiallyopposite ends of each of said first and second heat-transfer platesbeing cut into an angle shape each having two end edges, respectively,thereby defining a high-temperature fluid passage inlet by closing oneof said two end edges and opening the other end edge at axially one endof said high-temperature fluid passage, and defining a high-temperaturefluid passage outlet by closing one of said two end edges and openingthe other end edge at the axially other end of said high-temperaturefluid passage, defining a low-temperature fluid passage outlet byopening one of said two end edges and closing the other end edge ataxially one end of said low-temperature fluid passage, and defining alow-temperature fluid passage inlet by opening one of said two end edgesand closing the other end edge at the axially other end of saidlow-temperature fluid passage, and tip ends of large numbers ofprojections formed on opposite surfaces of the first and secondheat-transfer plates being brazed together, characterized in that anarrangement of pitches of said projections is different between axiallyopposite ends and an axially intermediate portion of each of said firstand second heat-transfer plates, and in areas facing said inlets andoutlets of said high-temperature fluid passage and said low-temperaturefluid passage, said arrangement of pitches of said projections in adirection substantially perpendicular to the direction of flowing offluid passed through said inlets and outlets is dense in an area portionnearer to a base end portion of the angle shape and sparse in an areaportion nearer to a tip end portion.
 5. A heat exchanger, comprising aplurality of first heat-transfer plates and a plurality of secondheat-transfer plates which are disposed radiately in an annular spacedefined between a radially outer peripheral wall and a radially innerperipheral wall, wherein a high-temperature fluid passage and alow-temperature fluid passage are defined alternately in acircumferential direction between adjacent ones of said first and secondheat-transfer plates, axially opposite ends of each of said first andsecond heat-transfer plates being cut into an angle shape each havingtwo end edges, respectively, thereby defining a high-temperature fluidpassage inlet by closing one of said two end edges and opening the otherend edge at axially one end of said high-temperature fluid passage, anddefining a high-temperature fluid passage outlet by closing one of saidtwo end edges and opening the other end edge at the axially other end ofsaid high-temperature fluid passage, defining a low-temperature fluidpassage outlet by opening one of said two end edges and closing theother end edge at axially one end of said low-temperature fluid passage,and defining a low-temperature fluid passage inlet by opening one ofsaid two end edges and closing the other end edge at the axially otherend of said low-temperature fluid passage, and tip ends of large numbersof projections formed on opposite surfaces of the first and secondheat-transfer plates being brazed together, characterized in that anarrangement of pitches of said projections is different between axiallyopposite ends and an axially intermediate portion of each of said firstand second heat-transfer plates, and said arrangement of pitches of saidprojections is set such that the unit number of heat transfer issubstantially constant in a radial direction at the axially intermediateportion of said first and second heat-transfer plates.
 6. A heatexchanger, comprising a plurality of first heat-transfer plates and aplurality of second heat-transfer plates which are disposed radiately inan annular space defined between a radially outer peripheral wall and aradially inner peripheral wall, wherein a high-temperature fluid passageand a low-temperature fluid passage are defined alternately in acircumferential direction between adjacent ones of said first and secondheat-transfer plates, axially opposite ends of each of said first andsecond heat-transfer plates being cut into an angle shape each havingtwo end edges, respectively, thereby defining a high-temperature fluidpassage inlet by closing one of said two end edges and opening the otherend edge at axially one end of said high-temperature fluid passage, anddefining a high-temperature fluid passage outlet by closing one of saidtwo end edges and opening the other end edge at the axially other end ofsaid high-temperature fluid passage, defining a low-temperature fluidpassage outlet by opening one of said two end edges and closing theother end edge at axially one end of said low-temperature fluid passage,and defining a low-temperature fluid passage inlet by opening one ofsaid two end edges and closing the other end edge at the axially otherend of said low-temperature fluid passage, and tip ends of large numbersof projections formed on opposite surfaces of the first and secondheat-transfer plates being brazed together, characterized in that anarrangement of pitches of said projections is different between axiallyopposite ends and an axially intermediate portion of each of said firstand second heat-transfer plates, and said projections are arranged atthe axially intermediate portion of each of said first and secondheat-transfer plates, so as not to line up in the direction of flowingof fluid passed through said axially intermediate portion.